Create Topo map using iphone?

[Nate W.]

Hi all,

I'm looking at a few vacant lots - one I already own and one I'm thinking about buying.  I'd like to create a quick and dirty topo map as part of my diligence to figure out if the lot is buildable given local ordinance.  Ideally, I'd just turn on the app, walk my property, and then the app would create a topographic map, and maybe provide some shading based on inputs like slope %.

I've used iphone apps like Gaia to import 3rd party topographic maps and map hikes using waypoints.  But after looking around, I haven't seen any of these apps built for real estate.  

Does anyone have a good app recommendation or a hack that I can use?  

Nate